Importance of γ′ shearing in low‐cycle fatigue of a wrought superalloy

AbstractThe present study deals with the fatigue behavior of a wrought nickel‐based superalloy René 41. Uniaxial, fully reversed low‐cycle fatigue tests were conducted at room and elevated (800°C) temperatures under total strain control. Cyclic response was analyzed using the statistical theory of the hysteresis loop, and scanning and transmission electron microscopies were employed to study relevant damage mechanisms. At room temperature, cyclic deformation was found to localize to slip bands since the first cycle, and most slip bands were formed very early in the fatigue life. Hence, shearing of the strengthening phase, coherent γ′ precipitates, was found to be significant only in the first few cycles. At 800°C, fatigue life was affected by an environmental attack resulting in a surface oxide layer. Cyclic deformation was less localized; nevertheless, cyclic slip localization in persistent slip bands and resulting γ′ shearing contributed to cyclic softening throughout the fatigue life.